In conventional motor driving systems, there are a drive variable speed driving system which drives a motor by a power supplied from an inverter, and a commercial driving system which drives a motor by a power supplied from a commercial AC power source. In addition, since a drive variable speed driving system can drive a motor while a rotation speed thereof is set to an optional value, a drive variable speed driving (or a drive variable speed operation) which drives (or referred to as operates, the same hereinafter) the relevant motor based on a speed reference designated from the outside of the drive variable speed driving system has been used.
The variable speed operation mode and the constant-speed operation mode may be used by switching in accordance with the speed command of the motor.
FIG. 3 is a timing chart showing an operation of a conventional motor driving system. The example shown in the drawing is an example of a case in which synchronous transfer to switch from drive variable speed driving to commercial driving, and synchronous capture to switch from commercial driving to drive variable speed driving are performed. Hereinafter, the description will be made with reference to this drawing.
In the drawing, a synchronous transfer processing is performed as described below by a system controller (not shown) which controls the motor driving system. The system controller sets a drive driving command (FIG. 3 (1), t1) so as to perform drive variable speed driving of a motor, and sets an external speed reference so as to set a rotation speed of the motor (FIG. 3 (2), t1). In addition, the external speed reference is an example of a case in which a speed reference is set from the outside of the inverter. By the above-described settings of FIG. 3 (1), (2), the rotation of the motor will start, and motor frequency and voltage increase gradually (variable speed driving FIG. 3 (4)), and when the speed of the motor reaches a speed set by the above-described external speed reference, the motor is continued to be driven at the speed (FIGS. 3 (4) t2-t3, drive variable speed operation).
When a commercial driving command is given in this state (FIG. 3 (3), t3) a synchronous transfer processing is performed in the following procedure.
(1) The motor is accelerated until a rotation speed (synonymous with a rotation frequency) thereof reaches a commercial speed (synonymous with a commercial frequency) (t3-t4)
(2) When the rotation frequency of the motor approaches to the commercial frequency, synchronization control to make a drive output coincident with phase and amplitude of the commercial AC power source is performed by phase synchronization control.
(3) Phase and voltage amplitude differences of the drive output and the commercial AC power source are within a setting value, and this state continues for a setting time (XFRDL: synchronous transfer switching speed delay time).
(4) After the state in the above-described (3) has continued for the setting time, a commercial output side circuit breaker 5 is closed (t5).
(5) The drive variable speed driving is stopped (t5).
(6) A drive output side switch (not shown) is tripped.
(7) The synchronous transfer has been completed.
(8) A commercial driving (commercial operation) is performed by the commercial output for a prescribed time (t5-t6).
In addition, at the time of the synchronous transfer, after the synchronous transfer switching speed delay time XFRDL according to the commercial synchronous transfer, a commercial side switch (not shown) is closed at a timing of t5, and the motor is switched to the commercial AC power source side. By this switching, a drive current is cut off (FIG. 3 (5)), and in addition, a commercial current is supplied (FIG. 3 (6)).
For a prescribed time (t5-t6), the commercial driving (commercial operation) by the commercial AC power source is performed.
In addition, when the commercial driving command is turned OFF, and the drive driving command is being given in this state (the same drawing (1), (3), t6), a synchronous capture processing is performed in the following procedure.
(1) When the drive output side switch is closed, the drive output is connected to the commercial AC power source, and thereby a phase synchronization circuit begins to operate.
(2) The phase synchronization circuit detects a frequency/phase/voltage amplitude of the commercial AC power source detected by a voltage transformer VT, and the operation is continued for a setting time (CPTDL: synchronous capture switching speed delay time), while a phase detection difference is within a setting value.
(3) After the state in the above-described (2) continues for the setting time, the commercial output side circuit breaker is tripped.
(4) The drive variable speed driving is started while the phase detected in the above-described (2) is made coincident with the frequency of the commercial AC power source (t7).
(5) The synchronous capture has been completed.
(6) The motor becomes in the drive variable speed driving state (t7-t8).
(7) The drive variable speed driving (drive variable speed operation) is performed by the drive output for a prescribed time (t8-t9).
In addition, at the time of the synchronous capture, after the synchronous capture switching speed delay time CPTDL according to the synchronous capture, the commercial side switch is tripped, and the motor driving is switched to the drive variable speed driving. By this switching, the commercial current is cut off at a timing of t7 (the same drawing (6), t7), and in addition, the drive current is supplied (the same drawing (5), t7).
As described above, in a motor driving system to perform commercial synchronous transfer which switches from drive variable speed driving to commercial driving or synchronous capture which switches from commercial driving to drive variable speed driving, it was necessary to set a drive driving command and a speed reference from the outside, and in addition, it was necessary to execute a commercial driving command.
However, even when the above-described commercial driving command is executed (commercial driving command ON), in order that the operation is actually switched to the commercial driving, it is necessary that after the commercial driving command was given, the rotation speed of the motor has reached the above-described speed reference, and after it was confirmed that the motor was accelerated till the speed of the motor reached the relevant speed reference, the prescribed synchronous transfer switching speed delay time is generated until the synchronous transfer is started. In addition, after the commercial driving, even when the commercial driving command is turned OFF in order to switch the operation to the drive variable speed driving, the synchronous capture switching speed delay time is similarly generated, and then the synchronous capture is performed. That is, the synchronous transfer to the commercial driving is not performed instantly in synchronization with the commercial driving command, but the synchronous transfer is performed after the variable speed driving was performed based on the external speed reference. Accordingly, even when the commercial driving command is substantially omitted, it is possible to obtain the same function, and it is possible to omit the related wiring by omitting the commercial driving command, and thereby an effect to simplify the motor driving system can be obtained.